A million women who take Britain's most popular contraceptive pills are being warned they risk developing potentially life-threatening blood clots.

GPs have been ordered to inform patients that they are almost twice as likely to develop blood clots if they take some of the most popular birth-control tablets, including Yasmin, Femodene and Marvelon, compared with older products.

The alert was sounded after scientists found that the so-called third generation contraceptives caused 14 deaths a year in France.

This comes after a review by the European Medicines Agency which found that the packaging of the pills should be updated to ensure that women are made aware of the risks of blood clots.

The MHRA wrote a letter to doctors on January 22 which stated that "there is no need for anyone who has been using a combined hormonal contraceptive without any problems to stop taking it on the basis of this review".

It added: "Combined hormonal contraceptives are highly effective in preventing unwanted pregnancy. They offer substantial benefits and these far outweigh the small risk of serious side effects."

Dr Sarah Branch, deputy director of the MHRA's vigilance and risk management of medicines division, said: "Women should continue to take their contraceptive pill. These are very safe, highly effective medicines for preventing unintended pregnancy and the benefits associated with their use far outweigh the risk of blood clots in veins or arteries.

"No important new evidence has emerged – this review simply confirms what we already know, that the risk of blood clots with all combined hormonal contraceptives is small.

"If women have questions, they should discuss them with their GP or contraceptive provider at their next routine appointment but should keep taking their contraceptive until they have done so."

The watchdog has written to the country’s 60,000 GPs telling them they must, for the first time, go through a patient checklist when prescribing the pills, according to the Mail on Sunday.

The aim is to prevent the pills being given to women with a higher inherent risk of developing blood clots.

The newer, third generation, of contraceptive pills are prescribed about two million times a year and have proved popular because they are less likely to cause sideeffects such as weight gain, headaches, breast tenderness and hair growth.

DVTs, which typically form in the leg, can travel up blood vessels to cause a potentially fatal blockage in the lung, known as a pulmonary embolism. They can also travel to the brain, triggering a stroke.

Risk factors include being older and overweight, smoking or being prone to a type of migraine.

Pharmaceutical giant Bayer, which makes Yasmin and Femodene, said it would be making blood clot warnings more prominent on its packets in the wake of the warning.

The warning letters have gone out to doctors across Europe, prompted by a report from France which found that from 2000 to 2011, 2,529 cases of serious blood clots – just over 200 a year – were down to combined contraceptives.

Of those, 1,751, or 146 a year, were due to third generation pills. These clots led to 20 deaths a year on average, 14 from newer versions of the pill and six from older versions.

That led the authorities in France to tell doctors to offer the newer pills only if their patients had first tried the old ones – a tougher response than the MHRA has taken.

Scientists are still investigating the link between the newer pills and serious blood clots, but they suspect that synthetic oestrogen used in the contraceptives may increase the risk.

The third generation pills were launched in the 1980s and official concerns were first raised about increased DVT risks in 1995.

Dr Asma Khalid, of Marie Stopes International, said: “Any method of contraception comes with its own benefits and possible side effects, and it’s important that women are given the information they need to make informed choices.”